Re: [rtcweb] Question about srtp_mki in DTLS/SRTP

[Simon Perreault <[e-mail]>]

On Wed, Jan 14, 2015 at 1:40 PM, Roman Shpount <[e-mail]> wrote:

> You can use the old key, until the first SRTP packet fails to verify, try
> to verify the SRTP packet using new key and record sequence number for this
> SSRC as the first sequence for which new key is used. For all subsequent
> packets use the new SRTP key. For all previous -- repeat the above process.
> This should work in the absence of MKI. At the end of the day this is
> simply optimization of trying to decode using multiple keys. You do need to
> maintain the list of old keys, time them out, and keep the sequence numbers
> for each SSRC where you start using each key.


Yes, that's the optimization described in the last paragraph of
https://tools.ietf.org/html/rfc5764#section-5.2. I didn't implement it
because I don't believe it actually optimizes anything. It certainly makes
code more complex, and could actually take more time to execute because of
branch misprediction.

Simon